The present invention relates to a method and apparatus for cutting sheet material, particularly limp sheet material such as cloth, paper, plastic and the like which is held in a spread condition while it is worked on by a tool such as a cutting blade, drill or other tool.
In the prior art, it is well known to spread cloth and other limp sheet materials on a support surface for cutting, drilling and other operations. In the garment industry it is known to spread cloth in single or multiple plies on a cutting table having an air-permeable bed, and to then cut pattern pieces from the material. The pattern pieces are then assembled in garments or other finished articles by cutting blades, lasers, water jets and other types of tools.
A conveyorized vacuum table formed with bristle beds for loading layups of one or more plies of sheet material onto the bed holds the layups in a compressed and stationary position under vacuum during cutting. The cut material is unloaded after the cutting operation is completed on one or more segments or "bites" of the sheet material. When the layup is held in place by vacuum, a plastic or other air-impermeable overlay is frequently placed on the layup to develop compression forces for compacting the material in addition to holding the layup in position.
Related pattern pieces are grouped into arrays called markers. A marker is usually a rectangular array and allows the related pattern pieces to be cut sequentially from a generally rectangular layup in a single cutting operation. A marker has an origin point, usually at a corner of the marker, from which the positioning of each pattern piece in the marker is referenced. Locating the origin of a marker on a layup therefore determines the location on the layup where the pattern pieces will be cut.
Cutting multiple markers involves significant fixed time costs that are independent of the specific pattern pieces in the markers. Two such fixed time costs are the time for the cutting tool to travel between markers, or "dry haul" time, and setup time to load the cutting table, which includes the time spent covering the material with the plastic overlay, loading the material onto the table, and advancing the material to the next bite.
Cutting multiple markers also requires consumables costs in loading the cutting table. A fixed amount of underlay and/or overlay material in used for each bite, regardless of the number or size of the pattern pieces to be cut from that bite. Some materials are provided in standard widths that are less than half the width of the cutting table. Much of the underlay and overlay material is therefor wasted in cutting these layups.
Some markers, such as those needed in producing T-shirts, also require symmetric features to be cut from a layup of tubular material. Accordingly, the marker must be precisely centered with respect to the layup. Otherwise, the cut pattern pieces will not be aligned with the axis of the tubular material and the resulting garment will be flawed.
Precise centering of a marker is also required when the material to be cut is ornamented, such as striped material. Markers that are not precisely centered with respect to the ornamentation will result in cut pattern pieces with misaligned patterns.
It would be advantageous to reduce the total fixed time and consumables costs in cutting multiple markers. It would also be advantageous to locate the origin point of the marker such that the centerline of the marker corresponds to the centerline of the layup.
It is, accordingly, a general object of the present invention to provide a method and apparatus for cutting multiple layups of sheet material positioned in a side-by-side relationship by combining multiple markers into a single marker.
It is a further object of the present invention to provide a method for cutting layups of sheet material where the origin points of the markers are registered relative to the center of the fabric.